The invention generally pertains to controllers for rotary drums and is applicable, for example, to a digital audio tape recorder having a rotary drum.
A rotary digital tape (DAT) recorder is a type of tape recorder that is capable of recording audio signals with a high density of packing of recorded information. In FIG. 5, there is illustrated a rotary drum 4 of such a DAT recorder, which DAT recorder is designated by the numeral 1.
A magnetic tape 2 recorded with DAT formatted audio data is unrolled from a supply reel of a tape cassette (not shown). The tape 2 is bent by a predetermined angle along a curved surface of the rotary drum 4 while guided by a pair of oblique guides 3A and 3B. After passing by the rotary drum 4, the tape 2 is rolled up onto a take-up reel of the tape cassette by way of a capstan and a pinch roller.
The drum 4 carries a pair of rotary heads 5A and 5B which are spaced 180.degree. apart from each other and have different azimuth angles relative to the tape 2. Each head scans an oblique track of the tape 2 as the drum 4 rotates. The DAT recorder 1 uses the rotary heads 5A and 5B to record and reproduce audio data to and from the magnetic tape 2.
A drum frequency signal FG.sub.DR indicative of the rotational speed of the rotary drum 4 and a drum phase signal PG.sub.DR indicative of a predetermined phase of the rotary heads 5A and 5B relative to the magnetic tape 2 are provided to a rotary drum controller of the DAT recorder 1 which controls the speed and phase of the rotary drum 4. For example, the drum phase signal PG.sub.DR is arranged to occur when one of the heads 5A and 5B reaches an edge of the tape 2.
The drum controller controls the phase of the rotary drum 4 by minimizing the phase difference formed between the drum phase signal PG.sub.DR (FIG. 6A) and a phase reference signal D.sub.REF (FIG. 6C) that is used for timing recording/playback operations of an internal signal processing LSI of the DAT recorder 1. Further, the drum controller controls the speed of the rotary drum 4 by measuring a period of the drum frequency signal FG.sub.DR (FIG. 6B) and converting the difference between the measured period and a reference period to a voltage to drive a drum motor.
It should be noted, however, that the drum phase signal PG.sub.DR occurs only once every complete revolution of the rotary drum 4. Because the drum controller controls the phase of the rotary heads 5A and 5B based on the drum phase signal PG.sub.DR, it can change the phase of the rotary heads only once per complete revolution of the rotary drum. Therefore, a relatively long time is required to establish the desired phase relation (synchronization) between the drum phase signal PG.sub.DR and the phase reference signal D.sub.REF.
This problem is particularly significant when a muted condition is released to initiate recording. Slow response of recording by DAT 1 often makes a user anxious or nervous.